1. Field of the Invention:
This invention relates to an agent for absorbing and releasing water vapor and more specifically, to an agent for absorbing and releasing water vapor, which agent has such hygroscopic capacity that varies significantly in degree depending on the temperature and releases water vapor easily when heated.
2. Description of the Prior Art:
No satisfactory methods have been proposed to date for the control in amount of water vapor in the air, namely, for humidity control or for the prevention of moisture condensation, for example, for the prevention of fogging. No development has hitherto been made as to sensors which can detect with good accuracy the humidity in the air, moisture condensation and the like.
In methods which have conventionally been relied upon for the control of humidity in a gas, the humidity control is primarily effected by operating an apparatus with two different types of functions, namely, dehumidification and humidification while making selective use of these two functions. Compared with temperature control, extremely complex apparatus and very irksome work are thus required for the practice of such conventional methods.
No complete solution has hence been provided as to problems which arise due to changes in room temperature in closed space featuring limited degrees of entry of the external air such as green houses, vinyl plastic hothouses, buildings and the like, such as moisture condensation. These problems have been inducing various troubles such as development of disease injury due to moisture condensation in green houses, malfunctions of electronic equipment such as computers in offices housed in buildings, etc. On the other hand, it is important to moisturize soil when raising crops on arid land or on soil having poor water-holding capacity. For this purpose, various moisturizing materials such as water-holding agents for soil have been investigated.
For the above-mentioned problems or demands, a new concept which is different from the conventional concept on air conditioning has recently been developed, for example, by making use of a hydrophilic polymer having hygroscopic capacity such as sodium polyacrylate or polyvinyl alcohol for the control of humidity or moisture. A variety of such hydrophilic polymers have been prepared on trial basis. Generally, these polymers have strong hygroscopic capacity. Their demoisturizing or dehumidifying capacity are thus strong. However, they are scarce of such capacity as maintaining given moisture or humidity levels or increasing moisture or humidity levels. They are therefore insufficient for moisture or humidity control. Except for the above-mentioned shortcoming, the moisture- or humidity-controlling method making use of such polymers has excellent merits in various aspects such as equipment cost, maintenance, installation space and the like, which conventional methods were unable to bring about.
Making use of their transparency, transparent materials such as inorganic glass, transparent ceramics and plastic materials have conventionally been used for various applications including for example window glass for houses and buildings, window glass for trains, tram cars and other passenger vehicles, mirrors, eye glasses, goggles, etc. As one of serious drawbacks of these products, may be mentioned that water vapor is caused to condense as minute droplets on their surfaces and as a result, the surfaces are clouded at hot and humid places. Various obstacles or troubles are developed especially when window glass, eye glasses, mirrors and the like are clouded on their surfaces.
A variety of attempts have been made to date for the solution of the above problem. For example, it has been studied to coat or spray various surfactants, polymers of hydroxyl-substituted (meth)acrylates, polymers of (meth)acrylates containing polyalkylene glycols substituted on their side chains, various silicon compounds such as dimethyl siloxane either singly or in combination. None of such methods are however fully satisfactory.
Turning to temperature sensors, a variety of materials led by bimetals have been known as materials for temperature sensors. They all enjoy good sensitivity and accuracy. A variety of sensors which are easy to use have thus been developed and are employed for various applications. Different from temperature sensors, no fully satisfactory humidity or dew sensors have yet been obtained despite of the development of various sensors because humidity is by itself correlated to temperature and no excellent detection method has been developed for the direct detection of water vapor.